This invention relates to fuser apparatus for electrostatographic reproduction machines and in particular to a fusing oil supply roll assembly having a fuser release agent management system.
In the process of xerography, a light image of an original document to be reproduced is typically recorded in the form of a latent electrostatic image upon a photosensitive member with subsequent rendering of the latent image visible by the application of electroscopic marking particles, commonly referred to as toner. The visual toner image can be either fixed directly upon the photosensitive member or transferred from the member to another support, such as a sheet of plain paper, with subsequent affixing of the image thereto in one of various ways, for example, as by heat and pressure.
In order to affix or fuse electroscopic toner material onto a support member by heat and pressure, it is necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become tacky while simultaneously applying pressure. This action causes the toner to flow to some extent into the fibers or pores of support members or otherwise upon the surfaces thereof. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be bonded firmly to the support member. In both the xerographic, as well as the electrographic recording arts, the use of thermal energy and pressure for fixing toner images onto a support member is old and well known.
One approach to heat and pressure fusing of electroscopic toner images onto a support has been to pass the print medium, with the toner images thereon, between a pair of opposed fusing rolls or roller members, at least one of which is internally heated. The opposed fusing rollers each have a length sufficient to handle different cross-track dimensions of print medium or copy sheets. During operation of a fusing system of this type, a copy sheet to which the toner images are electrostatically adhered is moved through the nip formed between the fusing rolls with the toner image contacting the heated or fuser roll of the pair, thereby to effect heating of the toner images within the nip. By controlling the heat transferred to the toner, virtually no offset of the toner particles from the copy sheet to the fuser roll is experienced under normal conditions. This is because the heat applied to the surface of the roller is insufficient to raise the temperature of the surface of the roller above a xe2x80x9chot offsetxe2x80x9d temperature of the toner. Ordinarily, at such a hot offset temperature, the toner particles in the image areas of the toner liquefy and cause a splitting action in the molten toner resulting in xe2x80x9chot offset.xe2x80x9d Splitting occurs when the cohesive forces holding the viscous toner mass together is less than the adhesive forces tending to offset it to a contacting surface such as that of the hot fuser roll.
Occasionally, however, toner particles will offset to the fuser roll due to an insufficient application of heat to the surface of the fuser roll (referred to as, xe2x80x9ccoldxe2x80x9d offsetting). It may also offset due to imperfections in the properties of the surface of the roll; or due to the toner particles insufficiently adhering electrostatically to the copy sheet. In any such case, toner particles transferred to the surface of the hot fuser roll are undesirable, and likely to be transferred subsequently to the backup roll during periods of time when no copy paper is in the nip.
In addition, toner particles can be undesirably picked up by the fuser and/or backup rolls during fusing of duplex copies or simply from the surroundings of the reproducing apparatus.
One arrangement for minimizing the foregoing problems, particularly that which is commonly referred to as xe2x80x9coffsetting,xe2x80x9d has been to provide a fuser roll with an outer surface or covering of polytetrafluoroethylene, known by the tradename Teflon to which a release agent such as silicone oil is applied, the thickness of the Teflon being on the order of several mils and the thickness of the oil being less than 1 micron. Silicone based (polydimethylsiloxane) oils which possess a relatively low surface energy, have been found to be materials that are suitable for use in the heated fuser roll environment where Teflon constitutes the outer surface of the fuser roll. In practice, a thin layer of silicone oil is applied to the surface of the heated roll to form an interface between the roll surface and the toner images carried on the support material. Thus, a low surface energy layer is presented to the toner as it passes through the fuser nip and thereby prevents toner from offsetting to the fuser roll surface.
A system of this type is described in U.S. Pat. No. 5,576,821, which was issued in 1996 to Xerox Corporation, the owner of the subject application. The disclosure of the xe2x80x2821 patent is incorporated herein by reference. In the xe2x80x2821 patent a release agent supply system consists of a roll of web material stretched between a supply roller and a take-up roller and having an application and oil supply roller positioned in between. The application and oil supply roller is positioned adjacent to the fuser roll and forms a nip therewith through which the web material passes. The web is impregnated with a release agent oil and supplemental oil is supplied on a continuing basis by the supply roller. The release agent oil is applied to the fuser roll as the web passes through the nip. The web moves through the nip by driving the take-up roller. The system of this patent is designed to apply the release agent as well as cleaning the fuser roll. To accomplish this the web material is moved across surface of the fuser roll in a direction which is opposite to the movement of the fuser roll.
In order to properly monitor the supply of web material and predict depletion, the web must be fed through the nip at a consistent speed. To accomplish this, the take-up roller drive motor is controlled by an algorithm which compensates for the changing overall diameter of the take-up roller. Premature exhaustion of the web material may occur because of an error between the actual diameter of the take-up roller and its calculated theoretical diameter, upon which the algorithm relies. These errors are caused by stretching, wrinkling, or contamination of the web material as it winds onto the take-up roller. It is a purpose of this invention to reduce the inaccuracies caused by errors in the actual diameter of the take-up roller and its calculated theoretical diameter.
To accomplish the purpose of this invention a release agent supply system is constructed adjacent to a fuser roll of an electrostatic printing machine. The release agent is supplied by a web material which is impregnated with an oil which constitutes the release agent. The web material is drawn over the fuser roll and engages the surface thereof to transfer oil from the impregnated web to the fuser roll. The web material is formed as a roll on a cylindrical reel which is mounted for rotation in advance of the fuser roll. The web material is stretched over the fuser roll to a take-up reel positioned on the opposite side of the fuser roll. In accordance with this invention an application roller is positioned between the supply reel and the take-up reel and is spring biased against the fuser roll to form a nip through which the impregnated web material extends. To improve accuracy in the relative movement of the fuser roll and the web material, the supply reel is driven. Since this reel is of a more predictable diameter, the accuracy of the release agent application process is improved. A consistent speed of the web material is obtained through the algorithm controlled drive motor and this results in more reliable monitoring. The take-up reel is also driven at a speed sufficient to maintain tension on the web material while avoiding stress that might cause damage.